The manufacture of stranded cable is well known within the wire and cable arts. Taking individual strands of electrical conductor wire and stranding them together provides a cable having a stable configuration and one which is more flexible than a solid conductor capable of carrying the same current load. One of the drawbacks to a stranded cable construction is in its inherent quality of providing a natural passageway for water and moisture to travel the length of the conductor. The interstitial spacings between the strands of conductor wire are natural conduits in which moisture travels. Eliminating this interstitial passageway in which moisture and water travel is known in the industry as "moisture blocking".
The manufacture of stranded moisture blocked electrical cable involves the assembly of a plurality of layers of components. Complex electrical conductor products can comprise multiple layers of stranded conductors encapsulated within multiple layers of special purpose insulation and jacket materials. Moisture blocking these complex constructions includes a material placed within the interstitial spacing of the strands of the conductor which inhibits the flow of moisture within the cable.
The manufacture of complex conductor products is typically accomplished in multiple stages. If the cable construction requires a stranded or bunched configuration, then conductor wires must be supplied to a stranding machine or buncher where they are stranded or bunched. If the construction requires a non-conducting or semi-conducting layer of plastic material in its configuration, this is typically applied in a subsequent step. If intermediate layers of concentric neutral wires are required, they are typically applied in subsequent steps. If a jacket layer is required, it, too, is typically applied in a subsequent step. If the construction calls for moisture blocking characteristics, that is to say, the cable is required to be constructed so as to prevent moisture from flowing longitudinally through the cable, a moisture blocking compound must be applied to the interstitial spaces of the stranded portion of the cable. Such a moisture blocking compound is typically applied to the conductor strands as they are configured or stranded for use within the cable construction. It is the testing of the uniformity and the continuity and effectiveness of the application of this moisture blocking compound which is the subject of the present invention.
The typical procedure for forming a simple water impervious, or moisture blocked cable includes the steps of: providing individual conductor wire strands to a stranding machine; placing water blocking compound on the wires which are to be stranded; stranding the wires which have been coated with the blocking compound; insulating the stranded cable; and placing a jacket over the whole assembly. It should be obvious that the manufacturing procedure of even a simple cable is very complex and very costly. It should also be obvious that if the moisture blocking compound were to be applied improperly, that is to say that it was applied in such a way that it did not block the flow of moisture within the interstitial spaces of the stranded conductor portion of the cable, the cable would be of no use for its intended water resistant application and would have to be scrapped.
Testing the moisture blocking characteristics of the cable is the only way to conclusively determine if it will meet the moisture blocking requirements set out in the specifications for its construction. The current practice in the industry is to test the moisture blocking characteristics of the cable after it is fully constructed. The test essentially comprises the steps of taking a three foot section of the finished cable and securing one end of it to a source of colored water and pressuring the water to between three and five pounds per square inch. The opposite end of the cable is then monitored with some clean, dry, absorbent, white paper which allows the technician performing the test to see if any of the colored water traverses the length of cable. This simple test checks the integrity of the water blocking compound and indicates whether it will function in its intended manner. However, this test has at least one major drawback. It must be performed on a fully and completely manufactured conductor. The stranded conductor wires must be "sealed" within the insulation and jacket before the test can be performed. The pressurized test water is forced down any interstitial spaces of the stranded cable conductor wires which have not been effectively sealed by the moisture blocking compound. The spaces outside of the stranded conductor wires are naturally filled with insulation material so that these spaces are effectively moisture blocked when the plastic is applied. The insulation material keeps the moisture from flowing along the outside of the stranded conductor wires.
These tests are performed on finished cables because if tests of the moisture blocking compound were attempted on uninsulated material, without the stranded conductor being supported by the plastic insulation and jacket layers holding the stranded conductor wires together, the stranded wires would simply disassemble. No test could then be performed because no stranded conductor wire assembly would exist.
Testing the moisture blocking characteristics of the moisture blocking compound applied to the interstitial spacings of the cable, before the construction has been completed, would allow the manufacturer to evaluate the quality of the stranded conductor portion of the cable before the balance of the expensive construction is completed. Such an evaluation could substantially eliminate scrapping completed cable due to improperly applied moisture block compound. The present invention is a method for testing the effectiveness and moisture blocking characteristics of stranded cable conductors after they have been stranded but before they are insulated or jacketed.